Air infiltration in walls with direct-fixed claddings

This research examines the extent to which drainage and ventilation drying can remove water that has leaked through claddings on walls with no specific drainage cavity. In this study, tracer gas and zonal computer models were used to measure and predict air infiltration in the space between the wall underlay and the cladding and in the insulated spaces in 16 wall specimens. Half of the walls were clad with weatherboards direct fixed to the frame over a synthetic flexible wall underlay, and the remaining eight had ‘barrier’ or sheet claddings. A companion paper describes drainage and drying measurements in the same walls. Tracer gas measurements showed that average infiltration through weatherboard claddings (0.2 L/s) was much higher than behind sheet claddings (0.03 L/s). The range of day-average infiltration measured behind weatherboards (0.02–1 L/s) actually overlapped earlier measurements in bottom-vented cavity walls (0.1–2 L/s), and this is thought to partly explain the successful track record of direct-fixed weatherboard claddings in New Zealand. The airflow characteristics of leakage paths through claddings and at junctions between the timber frame, cladding, lining and underlay were also measured and used in a zonal model to calculate infiltration rates into the insulated spaces and behind the different claddings. There was acceptable agreement between measured and calculated infiltration, and this supports the next step of applying the computer models to whole buildings to better understand the heat and moisture consequences of air infiltration in New Zealand walls.